The invention relates generally to an improvement in an axial piston pump and more specifically to a spline configuration which ensures constant alignment of the pump components which are subjected to varying unbalanced axial and radial forces at varying combinations of rotational speeds and pressure loads.
The axial piston pump has been the subject of numerous improvements and patents. Generally, such a pump comprises a cylindrical barrel in which a plurality of pistons are concentrically disposed about the barrel axis and slidably mounted in cylinders in the barrel for reciprocal motion parallel to the barrel axis. Reciprocal motion is imparted to the pistons by a swash plate which is adjustably inclinable with respect to the axis of the barrel.
A stationary valve plate positioned immediately adjacent the end of the barrel opposite the swash plate contains intake and discharge channels which are in alternating sequential registry with the cylinder volumes as they fill and pump hydraulic fluid, respectively.
An ever present problem to which axial pumps are subject involves the bowing or lateral deformation of the drive shaft caused by the uneven forces to which it is subjected. These uneven forces are reaction forces associated with the load imposed by pumping of the hydraulic fluid during that portion of barrel rotation in which the pistons are advancing into the cylinders. These uneven and unbalanced forces tend to produce bowing of the drive shaft and tilting of the barrel relative to the valve plate. The common manifestation of such skewing is leakage of hydraulic fluid between the valve plate and the barrel. The resulting leakage may be minor or it may increase at high operating pressures to the extent that the efficiency of the pump is severely impaired. This condition, at best, is undesirable and in certain applications can be hazardous.
A solution to the problem of barrel-valve plate separation and fluid leakage utilized in many prior art designs comprises a floating mounting of either the barrel or the valve plate. The alternate component is fixedly mounted and this arrangement is intended to maintain planar alignment of the faces of the valve plate and barrel. A relatively tight seal is thus intended to be maintained between them and leakage is expected to be minimized over a broad range of operating conditions.
It has been found, however, that the barrel-valve plate misalignment problem is highly complex. Not only is the barrel subject to forces which tend to angularly skew it with respect to the valve plate, but it is also affected by unbalanced forces which tend to translate the barrel radially. Furthermore, these forces have been found to vary widely with the rotational speed and the instantaneous delivered hydraulic pressure.